(At around one hour and twenty-two minutes) When Draco Malfoy says "I didn't know you could read" to Harry (looking like Goyle with polyjuice potion) it was actually improvised, because Tom Felton forgot his line.

(At around fifteen minutes) The opal necklace, which plays an important role in Harry Potter and the Half-Blood Prince (2009), can briefly be glimpsed inside a display case in Borgin and Burkes' shop in Knockturn Alley when Harry first enters.

The Weasley's car is a Ford Anglia. This is the same color and model car that J.K. Rowling, and her best friend from school, used to ride around in when they were younger. She used the car for the book, and later the movie, out of her fond memories of driving in it.

During production, Emma Watson frequently brought her pet hamster Millie on set. Unfortunately, Millie passed away shortly after shooting began. The Set Department created a specially-made hamster coffin, complete with velvet lining, and the name "Millie" engraved on the top. "I don't think a hamster has ever had a better send-off", Watson said.

It was Jason Isaacs' idea to have Lucius Malfoy sport long blond hair, as well as carry a walking stick, inside of which, he would conceal his wand. He grew attached to the walking stick, and at one point tried to walk off with it, though he was caught.

Daniel Radcliffe was initially only offered one hundred twenty-five thousand pounds (approximately one hundred eighty-one thousand five hundred dollars) for this film. The actors' union, Equity, stepped in and negotiated new terms, which increased his salary to roughly two million pounds (three million dollars).

(At around twenty minutes) A gag from the book is rendered incomprehensible in the film, due to a lack of information. While chatting with the Grangers at the bookshop, Mr. Weasley says, "I understand that other Muggles are afraid of you." This is because they are dentists.

Rupert Grint has such a severe case of arachnophobia, he has still not watched the entire scene where Ron and Harry are in Aragog's hollow. In that scene, Ron's frightened look, and his uncomfortable squirming throughout, was not from acting, but from Rupert being legitimately terrified at even the thought of spiders.

The animatronic Phoenix used to portray Fawkes looked so lifelike (despite the fact that Phoenixes are mythical creatures), that Sir Richard Harris (Professor Albus Dumbledore) thought it was a real living bird when he first saw it.

(At around seventeen minutes) When Hagrid (Robbie Coltrane) is escorting Harry (Daniel Radcliffe) out of Knockturn Alley, and again when Lockhart (Kenneth Branagh) turns to show his other profile to the photographer, hardcover editions of Harry Potter books can be seen on the shelves.

Director Chris Columbus instructed Cinematographer Roger Pratt to bring a darker look to the film, reflecting the darker tone of the story. Hence, the sets were lit with more subdued lighting, and the color palette was desaturated a bit. These changes would continue throughout the franchise, with each film getting darker and increasingly desaturated.

Lucius Malfoy originally was not supposed to have long hair, however, when Jason Isaacs was cast in the role, he requested the longer hair, so that he could be distinguished from his son Draco. In order to keep the hair from falling in front of his face, Isaacs had to keep his head tilted back, which further added to the snobbishness of the character, as it made him appear as if he was "looking down his nose at everyone."

The set for Dumbledore's office was, at the time of its construction, the most expensive set built for the films. Chris Columbus and Production Designer Stuart Craig agreed that, as headmaster, Dumbledore should have the most elaborate office possible. However, they were informed that the proposed design, with its massive stone columns, bookcases, curio cabinets, paintings on the walls, tables filled with various objects, antique desk, throne-like chair, and a giant telescope, would be far too expensive to produce. The producers ultimately were able to secure the funds needed to build the set.

During post-production, Producer David Heyman went to visit Sir Richard Harris in the hospital. Though he was very weak from his illness, Harris insisted that the role of Dumbledore not be re-cast. Sadly, Harris passed away shortly before production was to begin on the next film, necessitating a re-cast.

Many people think that Professor Gilderoy Lockhart is a character based on J.K. Rowling's ex-husband. Rowling has said, on her official website, that Lockhart is based in an egocentric person that she really dislikes, but he is not her ex-husband.

Zoë Wanamaker does not appear in this film as Hogwarts' flying instructor, Madam Hooch, as Wanamaker found the salary unsatisfying. Her character was written out by giving Hooch's speaking lines to Professor McGonagall (Dame Maggie Smith) and other characters.

On an episode of Have I Got News for You (1990) broadcast around this film's release, the panelists discuss an article claiming that the Russian President (later Premier) Vladimir Putin was deeply disturbed and offended that Dobby the House elf seemed to have been created in his image. There is an undeniable resemblance either way.

(At around eleven minutes) In order to create a realistic image of the floating set of needles (knitting in The Burrow), one of the crew coerced his mother to let them film her for several hours as she did her own knitting.

The film earned over eighty-eight million dollars in the U.S. on its opening weekend, which at the time placed it third in the list of all-time biggest openings, behind Spider-Man (2002) and Harry Potter and the Sorcerer's/Philosopher's Stone (2001).

A theater manager in Stavanger, Norway reported that the film was making his younger patrons ill. Evidently, many children who had overindulged on sweets and popcorn, were throwing up when Ron begins vomiting giant slugs. "It is not a particularly fun task for our employees to have to wash away the sick", he said.

(At around one hour and nineteen minutes) During the filming of the scene where Crabbe and Goyle eat the floating cupcakes, Jamie Waylett and Josh Herdman cut their mouths on the hooks which were used to attach the cupcakes to the fishing line that was holding them up.

The various bookcases and cabinets in Dumbledore's office actually concealed removable walls (known in the film industry as "wild walls") that allowed the cameras to have enough room to be able to shoot from various angles, as the set, despite its grandiose appearance, was rather cramped.

Jason Isaacs originally auditioned for Gilderoy Lockhart, but Chris Columbus asked him to try for Lucius Malfoy too. Isaacs didn't want to, because it was too similar to his role as Captain Hook in Peter Pan (2003) , but was too polite to say no. When he was offered the part, Isaacs almost turned it down, but family members convinced him to do it.

The train station interior used in the film is King's Cross in North London, whereas the exterior shot is actually St. Pancras. The two stations are adjacent to one another, but not the same building. This was done because the architecture of St. Pancras is much more visually appealing.

Due to scheduling conflicts, John Williams was not able to deliver a fully elaborated score. Composer William Ross was hired to adapt Williams' material, to complete the film's score, and was subsequently conducting the orchestra during the recording sessions.

In his appearance on 8 Out of 10 Cats (2005), Alan Cumming revealed that he had been offered the role of Gilderoy Lockhart in the film, but when he learned from his agent, how much more money Rupert Grint, with whom he shares an agent, would be getting paid, he refused to sign on, as he would not agree to be paid less than "a twelve-year-old amateur!"

Chris Columbus was unsure about Jason Isaacs' ideas for Lucius Malfoy's costume, hair, and voice. It was Daniel Radcliffe who commented that he thought the changes were "really cool", and Columbus went along with it.

(At around one hour and thirteen minutes) The spell to open Dumbledore's office is Sherbet Lemon. That is a hint to the first book, where Dumbledore admits that he grew quite addicted to sherbet lemons.

One of Chris Columbus' daughters had trouble reading, until she read Harry Potter and the Sorcerer's/Philosopher's Stone in two days, which opened her eyes to the world of books. After reading the Chamber of Secrets, she asked her dad to make films out of them, but there were fifty other directors already interested. Columbus fell in love with the first two books as well.

In order to prevent damage to the five-hundred-year-old building, a false wall was erected at Gloucester Cathedral for the scene in which Harry and his friends discover the message from the Heir of Slytherin written on the wall.

Jason Isaacs provided the voice of the basilisk calling to its victims. Chris Columbus thought Isaacs was so good at doing voiceover work, he asked him to create a creepy sounding voice for the basilisk, considering the book only describes it as a hissing sound.

The first name of the character of Salazar Slytherin is based on the former Portuguese dictator Salazar, as it was in Portugal, and namely the city of Oporto, where J.K. Rowling had the idea and wrote her favorite parts of the first Harry Potter book.

Despite the fact that Crabbe and Goyle have more screentime in this film than any of the others, they have no dialogue, as their voices were dubbed over by Daniel Radcliffe and Rupert Grint for the Polyjuice Potion sequence.

Chris Columbus was amazed how beautifully Daniel Radcliffe, Emma Watson, and Rupert Grint matured over the Harry Potter franchise, compared to some child actors and actresses, who start out adorable, and then either lose that, or become bad actors and actresses as they grow older.

Through advance ticket sales at Odeon Cinemas, this film generated more than one million pounds (roughly two hundred thousand tickets) before its release in the UK. An additional eight million pounds was generated through preview showings at UK cinemas (both Odeon and non-Odeon).

In recalling his father reading the first two Harry Potter books to him, Daniel Radcliffe stated that his father had a great voice for the Basilisk. He suggested his father to Director Chris Columbus and his father was mortified.

Even though Tom Riddle is played by two different characters Tom in this film looks slightly less human than he did when confronting Slughorn about Horcruxes. In fact this scene is implied to take place after Tom got his answer on Horcruxes. If one looked closely in the Half Blood Prince film a brief shot shows a young Tom Riddle in pain suggesting he split his soul for the first time. According to Dumbledore the more Horcruxes Voldermort made the less human he became so that being the likely outcome Myrtle died after the Slughorn scene and Tom used her murder to make his first Horcrux namely the diary.

(At around one hour and twenty-nine minutes) When Tom Riddle sucks Harry into his diary, taking him back fifty years, the date is the 13th of June. This is a clever insertion, as from the point in time when this happens in Harry's second year, dating it back fifty years to the 13th of June, was in fact a Friday.

Ironically, the Basilisk that Voldemort had plotted to use to purge Hogwarts of Muggle-borns and Harry was used against him by having her venom destroy most of his Horcruxes, which led to his Final Downfall and Death. Even more ironic, Voldemort's Horcruxes that were not destroyed by the Basilisk's venom were each destroyed by Vincent Crabbe and by Voldemort himself.

At no point in the series was it explained how the Basilisk sustained itself. While Acromantulas feared it, they never described the serpent preying on them, and despite her bloodthirsty nature, the Basilisk never fed on any of its victims. That was especially noteworthy, because on the night it attacked Mrs Norris, it said "So hungry for so long".

In 2017, in celebration of the 20th anniversary of "Harry Potter" franchise, arachnologists Anton A. Nadolny and Alireza Zamani named a new species of Iranian wolf spiders (Lycosidae) after Aragog, as Lycosa aragogi. The single specimen was collected on April 26, 2016, almost 19 years to the day after Aragog died (April 20, 1997 in the world of the book), according to the "Harry Potter" series, by J.K. Rowling.

Caio Cesar, a prominent Brazilian voice actor, who dubbed Daniel Radcliffe as Harry Potter and in other films, was also a military cop, and died at the age of twenty-seven, in 2015, after being shot at the Complexo do Alemão slums, in Rio de Janeiro.

At the beginning of the movie, Harry is looking through the photo album he'd received from Hagrid at the end of the first movie. The first photo he sees is of his parents, James (Adrian Rawlins) and Lily (Geraldine Somerville), holding Baby Harry (Saunders Triplets). None of them was credited.

When Chris Columbus scripted Young Sherlock Holmes (1985), Watson believed Holmes obsessed over a case, because unlike other boys his age, even at Christmas, he had no family to which to go home, like Harry Potter or Kevin McCallister, and Columbus has ties to both the Harry Potter and Home Alone franchises.

Throughout the eight-movie series, five actresses played "Pansy Parkinson": 1. Katherine Nicholson (Harry Potter and the Sorcerer's/Philosopher's Stone (2001), and this movie, uncredited in both). 2. Genevieve Gaunt (Harry Potter and the Prisoner of Azkaban (2004)). 3. Charlotte Ritchie (Harry Potter and the Goblet of Fire (2005), originally listed as "Student", and uncredited)). 4. Lauren Shotton (Harry Potter and the Order of the Phoenix (2007), uncredited again as Pansy. 5. Scarlett Byrne in Harry Potter and the Half-Blood Prince (2009), Harry Potter and the Deathly Hallows: Part 1 (2010), and Harry Potter and the Deathly Hallows: Part 2 (2011).

Harry used Arania Exumai, a stunning or killing spell for use against spiders, while attempting to escape the Acromantula colony. He learned the spell from Tom Riddle upon visiting the latter's sixteen year old memory in his diary. The spell was never mentioned in the book.

According to Harry Potter: The Creature Vault, Aragog "was such a beloved character that the design crew wore black armbands while the spider's final scene (Aragog's funeral) was filmed" during Harry Potter and the Half-Blood Prince (2009).

This is the second time and the second film Harry and Ron get detention. Harry receives detention two more times in the Order of the Phoenix under Umbridge for telling 'lies' and teaching 'Dumbledore's Army'. Ron and Hermione gets detention for the third & second time respectively in the latter film for being part of 'Dumbledore's Army'.

Just after Dobby causes the pudding to fall on top of Mrs Mason a picture of a young boy with blonde hair can be seen on a table next to Harry. The boy in the picture strongly resembles Kevin McAllister who is the main character in the first two Home Alone films. Christopher Columbus who directed the first two Harry Potter films also directed the first two Home Alone films.

There is a discrepancy in the description of the size of the basilisk between the novel and film versions, with the snake being implicitly described as being much larger in the latter. At the end of chapter 16 of the novel, when Harry, Ron and Lockhart find the snakeskin in the novel, the narration states that "the creature that had shed it must have been twenty feet long at least." In the corresponding scene in the film, Ron states "whatever shed this must be 60 feet long. Or more".

In the film Filch sits outside the Great hall and waits for Harry and Ron to show up after they arrive by car. This similarly happened in the book version of the Philosopher's Stone where Filch caught Harry and Hermione after they helped Hagrid dispose Norbert and even says the same line that they are in trouble. The only difference is that Ron is in trouble in this film.

Although an average basilisk is said to have an average lifespan of 900 years Salazar Slytherin's Basilisk lived for approximately 1000 years, being there since Slytherin built the Chamber of Secrets around that time.

It has been theorised that spiders fear basilisks because arachnids can see 360-degrees around them and cannot shut their eyes, leaving them extremely vulnerable to the monster's killing gaze, although this theory does not explain why frogs and dragonflies do not fear the basilisk, as they have an even greater field of vision.

The Acromantulas more closely resemble wolf spiders (family Lycosidae) than actual tarantulas (family Theraphosidae), but that may reflect upon the fact that wolf spiders were the first kind of spider to ever be referred to as "tarantulas".

Aragog was falsely accused by Tom Riddle for the Petrification of many students before the death of Myrtle. Acromantula are not known to be able to induce petrification, making this is another lack of insight of the justice system of the Ministry of Magic, as they fail to notice the discrepancy.

Wearing glasses will not protect a person from the fatal effect of the basilisk's stare, because glasses still allow one's line of vision to connect directly and clearly with the serpent's eyes, unlike looking in a mirror or through a camera.

Even though Fawkes saved Harry from dying with phoenix tears the Basilisk could had destroyed the piece of Voldermort's soul in Harry as Harry was a Horcrux at the time although this is not revealed until the Deathly Hallows.

Various medias have shown both the male and female depictions of the species for Slytherins Basilisk, in the book,it seemed to be female:when Harry first saw it,he described it as "vivid,poisonous green" but made no mention of a red crown,which implied that either it had one and he simply didn't see or that the Basilisk was female, that was further supported by Pottermore which depicted the Basilisk with a distinct lack of a crown,red or otherwise. Though the voice Harry "hears" in the film sounds male, the Basilisk in the film likewise seems to lack a distinctive crown on its head.

Spoilers

The trivia items below may give away important plot points.

(At around two hours and twenty-five minutes) The script originally said that Hermione would hug Harry and Ron in the final scene. As the eleven-year-old Emma Watson was embarrassed about having to hug the boys in front of the entire cast, Chris Columbus allowed her to change the scene so that Hermione just hugs Harry, then starts to hug Ron, but the two get embarrassed, and resolve by only shaking hands. Watson also stated in a recent interview, that she kept letting Daniel Radcliffe go too quickly, so the film was "frozen" for a few seconds to make the hug look like it lasted longer than it actually did. Her hesitation with Ron is also taken by fans as a precursor to the relationship that will develop between the two characters.

(At around two hours and five minutes) Foreign language translations had to change Tom Marvolo Riddle's name, so that an appropriate anagram could be formed: In Spanish, his name became "Tom Sorvolo Ryddle", which transforms into "Soy Lord Voldemort". In French, his name is "Tom Elvis Jedusor", which becomes "Je suis Voldemort". In Dutch, his name is "Marten Asmodom Vilijn", which is an anagram for "Mijn naam is Voldemort". In Turkish, the name is "Tom Marvoldo Riddle", which makes up "Adim Lord Voldemort". In Brazilian Portuguese, the name is "Tom Servolo Riddle", which makes up "Eis Lord Voldemort". In Danish, his name is "Romeo G. Detlev, Jr.", which makes up "Jeg er Voldemort". In Italian, his name is "Tom Orvoloson Riddle", which makes up "Son io Lord Voldemort". In German, his name is "Tom Vorlost Riddle", which makes up "Ist Lord Voldemort". In Icelandic, his name is "Trevor Délgome", which makes up "Ég er Voldemort". In Swedish, his name is "Tom Gus Mervolo Dolder", which makes up "Ego sum Lord Voldemort" (which is actually in Latin).

(At around one hour and sixteen minutes) When Hagrid charges into Dumbledore's office to defend Harry, he is carrying a dead rooster in his hands. This is in reference to a scene in the book (cut from the movie), where Hagrid finds all the roosters dead. The sound of a cock-crow is fatal to a basilisk.

(At around two hours and twenty-five minutes) When Lucius Malfoy tries to curse Harry at the end, he mutters,"Avada..." As mentioned in the fourth book, this is the beginning of an Unforgivable Curse named Avada Kedavra, or the killing curse. This rather makes it look like Malfoy is stupid enough to actually try to kill a child in the middle of a school, chock full of students and teachers, with no means of escaping. But as Jason Isaacs has explained in several interviews, the novel mentions no specific spell for him to use and, since he had just been reading the fourth book at the time, this was the only curse he could remember. So, as it turns out, Dobby saved Harry's life in this scene.

Chris Columbus wanted the movement of the camera to be snake-like, reflecting the basilisk's movement throughout the castle. Hence, certain scenes were filmed using hand-held cameras, which allowed for more fluid camera movement, and Columbus at one point, actually steered the camera operator (by holding him by the shoulders), in order to get the shots exactly where he wanted them.

(At around thirty-three minutes) Although the subplot, which involved Percy Weasley and Penelope Clearwater (when Ginny discovered them kissing, and promised not to tell anybody) was cut, while Nearly Headless Nick is on his way to the Great Hall, he does say: "Hello Percy, Ms. Clearwater," to the couple as they walk out.

The filmmakers assumed that the Chamber of Secrets' only appearance would be in this film. However, the Chamber ends up making a second appearance in Harry Potter and the Deathly Hallows: Part 2 (2011). Since the set had been dismantled, it had to be constructed again.

(At around one hour and twenty-four minutes) When Harry and Ron are under the Polyjuice Potion, and interrogating Malfoy, he asks Goyle (Harry), if a small wrapped gift is his, and he answers no. However, in numerous freeze frames throughout the movie, the gift can be seen in Harry's possession.

(At around one hour and twenty-one minutes) In the book, the Polyjuice Potion changes a person completely, including his or her voice. You will notice that there was no change in Mad-Eye Moody's voice in Harry Potter and the Goblet of Fire (2005). Harry and Ron do not have to disguise their voices when they confront Malfoy, but instead have to be careful about the way that they talk, in order to sell their identities of Crabbe and Goyle, so that Malfoy doesn't suspect anything.

While writing "The Deathly Hallows", J.K. Rowling was seriously considering bringing the Ford Anglia back to defend Ron, from a pair of Death Eaters that corner him on the castle grounds. The car was to emerge from the forest, and run the Death Eaters straight into a wall of the castle, the cars lights then gave out slowly as if it died, but then J.K. Rowling opted out of it, as she thought the Ford Anglia would most likely have been destroyed due to living in the forest for too long, and the idea itself seemed childish to her.

(At around one hour and twenty-eight minutes) When Harry speaks to Tom Riddle by writing in the diary, the handwriting seen isn't that of Daniel Radcliffe. Chris Columbus didn't feel that Radcliffe's handwriting was how Harry would write, so an extra's handwriting was used instead.

Bonnie Wright revealed that she filmed a scene, in which Ginny strangles roosters outside of Hagrid's hut. In the book, it was revealed that Ginny, under Tom Riddle's influence, killed Hagrid's roosters, since the crow of roosters is fatal to the basilisk. This fact is entirely omitted from the film, therefore the scene was cut.

(At around twenty-one minutes) Lucius Malfoy slipped Tom Riddle's diary into Ginny Weasley's book basket, in the book shop, after demeaning her for her secondhand book. It is behind the book he first took out of the basket.